The ability to supply energy is of paramount importance to nearly all daily activities: Transportation, communications, manufacturing, provision of services, agriculture, all of these require energy. In addition to the supplying of energy, it is necessary that the energy be delivered at a rapid enough rate for the given application. This is power.
As more and more energy has been needed for the above applications, the sources, the raw materials so to speak, of many easy-to-use energy forms have been dwindling. Many sources are non-renewable, such as those based on fossil fuels, such as coal and oil. Additionally, these energy sources are also needed as raw materials, not for energy, but for manufacture of goods. Petrochemicals, such as plastics, are prevalent in today's world, but they take away from the sources of energy. An additional limitation on the use of fossil fuels for energy sources by conventional means, is that most technologies depend upon combustion of the fuel, and combustion reactions are limited by the Carnot cycle to about 30% efficiency.
Other raw materials, such as radioisotopes are abundant and could provide for energy needs for long into the future, but are less easy to use. Self-sustaining reactions such as fusion are extremely difficult to achieve and to manage once achieved.
Although man has gradually turned more and more toward renewable resources, many of the old mainstays are chosen to be used in different form. Often these are to some extent renewable. Hydrogen is the principal component of hydrocarbon fuels and is usable in different forms. As fossil fuels, it is limited. However, of particular importance, hydrogen is a component of alcohols, which are derived on a renewable basis from plant sources.
While hydrogen is plentiful as a component of water, the energy required to obtain it is greater than that which it will later release. In such cases, it is economical only to generate hydrogen using high efficiency power sources. However, hydrogen is highly suitable for providing energy in areas that do not have an energy source and, as such, serve to move the energy from where it is generated to where it is needed, in much the same way that power lines move electrical energy from the source generating plant to the end user.
As mankind has progressed, much of life takes place in a mobile fashion. Transportation is critical, but so is the ability to carry along portable sources of energy, such as batteries and fuel cells. Heretofore, batteries have been the choice. Often these are single use, basically carrying their energy with them in the form of chemical compounds. Other batteries are rechargeable, but these require a source of electrical energy to be recharged.
Most batteries are of the type that requires both a fuel and an oxidizer to be carried around. More recently some battery types, similar to fuel cells, have come to the foreground that carry only the fuel and use the air around them as the oxidizer.
Fuel cells, on the other hand, can provide electrical energy and can be recharged by use of chemical fuels that contain hydrogen. Fuel cells require a fuel to be provided, but use the surrounding air as their oxidizer. The byproducts of reaction in the fuel cell are predominantly water, and must be removed from the cell to keep it operating. (While the use of fuel in a fuel cell is often described as “burning”, it is an electrochemical reaction and is not related to combustion. Thus, fuel cell efficiency is not limited by the Carnot cycle.) Fuel can be continuously fed without downtime, such as that required to change batteries. Additionally, the fuel source for fuel cells are typically much less expensive than the materials that provide the energy source in batteries.
Fuel cells can be made in small or large configurations. The larger designs are typically used as stationary energy sources, while the smaller ones are suited to portable applications. Some fuel cells are used in remote locations, where the fuel is brought to them periodically, but where they continue to provide electrical energy constantly.
There are several different types of fuel cells. The more important ones for the present invention are proton exchange membrane fuel cells (PEMFC), direct methanol fuel cells (DMFC), and solid oxide (SOFC) fuel cells. The technologies vary in different designs, different materials used for electrolyte/anode/cathode, different fabrication processes, different operating parameters, including fuels and operating temperatures, and are suited for different applications.
At the present time, the manufacture of fuel cells takes place by making individual cells and then incorporating these cells into a stack of cells to provide the surface area necessary to provide adequate power to the utilizing device.
The present invention describes fuel cells of the PEMFC/DMFC and SOFC types and details methods of manufacture that relate to PEMFC/DMFC and SOFC technologies in particular, but which may also be suitable for other types of fuel cell systems. Furthermore, the present invention allows for the manufacture of a multiplicity of cells together in a single solid unit.
Various techniques are presently used to make fuel cells. Typically, these rely on making fuel cells units and then putting them together into stacks to increase the voltage or current to that which is required for the application. One recent technology that may be used is that of rapid prototyping. Rapid prototyping is the name given to a methodology that uses different technologies to take a computerized design and make a three-dimensional physical model. Models made by rapid prototyping are often used in design testing, to make tooling, or in a few applications, to make products for sale.
In rapid prototyping, a design is generated and then computer processing is used to cut the design into thin slices, much like a microtome cuts tissue samples. These thin slices, typically 0.1 mm and thinner, are then laid down to build the three-dimensional form, by use of various processes and materials in succession to build up layers until a sold three-dimensional object is fully constructed.
A very important feature of rapid prototyping is that it is an “additive” process. Additive processes are much less material intensive than subtractive processes. Thus, additive processes are typically less costly and produce less waste. Additionally, through rapid prototyping, selective processes may be incorporated that only are applied to a given area of the article being manufactured.
An example of a subtractive process is the etching of copper-clad electronic circuit boards, which begin as a solid sheet of copper on a substrate. By coating with a photo resist, and then exposing to a pattern, the pattern is transferred to the copper. Areas that are not part of the pattern do not have photo resist that is cured on them and they can then be removed by etchant. The cost of lost copper is significant. A corresponding additive process from the same industry is one in which copper is deposited selectively in the form of the pattern on the circuit board substrate. In this fashion, only the necessary copper is “added”, with essentially no waste.
While rapid prototyping is usually used for making solid mockups, it has rarely been used for production articles.
As computerized manufacturing becomes more sophisticated, it ahs become possible to utilize rapid prototyping, particularly where the size of the component to be made is small. Such a suitable product is a micro fuel cell.
The present invention utilizes the concept of rapid prototyping and takes it a step further to fabricate fuel cells in production quantities that are ready to use and do not have to be assembled from a stack of individual planar cells.